1. Field of the Invention
This invention relates to the manufacture of .alpha.-cyano-ethylated aliphatic aldehydes by reaction of acrylonitrile and an aldehyde in the presence of an alkali metal hydroxide. More particularly, this invention relates to a process wherein the acrylonitrile and aliphatic aldehyde are in contact with the alkali metal hydroxide for only a brief period of time and reaction product is separated from the alkali metal hydroxide and unreacted acrylonitrile and aliphatic aldehyde is recycled. The process is conducted in a tubular reaction zone which can be vertical or horizontal at a temperature of 20.degree. to 120.degree. C.
2. Discussion of the Prior Art
In the presence of alkaline catalysts, acrylonitrile reacts with aldehydes, the .alpha.-carbon atoms of which possess one or two hydrogen atoms, forming 3-substituted propionitriles (U.S. Pat. No. 2,353,687). This so-called "cyanoethylation" reaction also occurs with other compounds which have an active hydrogen atom. For example, 2-ethyl butyraldehyde and acrylonitrile react in the presence of catalytic amounts of 50 percent caustic potash solution forming 2-(.beta.-cyanoethyl)-2-ethyl butyraldehyde. A yield of 76.6 percent results after a reaction period of 4.5 hours. (H. A. Bruson, Th. W. Riener, J. Am. Chem. Soc., 66, 57 [1944]). The reaction is strongly exothermal. Acetaldehyde reacts with acrylonitrile in the presence of a 50 percent caustic soda solution forming .gamma.-formylpimelonitrile. For a yield of 40-50%, the reaction period amounts to 2-3 hours. Under the same conditions, propionaldehyde forms 4.9 percent 2-methyl-4-cyanobutyraldehyde (U.S. Pat. No. 2,409,086). 2,2-dimethyl-4-cyano-butyraldehyde is formed in up to 60 percent yield from the reaction between isobutyraldehyde and acrylonitrile.
The well-known processes for cyanoethylation of aliphatic aldehydes proceed with only moderate selectivity and require long reaction times, therefore considerably impairing the economic efficiency of the processes. This disadvantage can not be eliminated by an increase in the concentration of the catalyst, as the reaction becomes more violent leading to polymerization or condensation reactions of the alkali sensitive starting materials.
It is, therefore, an object of the invention to provide a process for the preparation of such cyanoethylated products in the shortest possible reaction time and with a high yield.